The present invention relates a method for identifying a position of a vehicle on a road using GPS (Global Positioning System), and in particular, to a method for detecting or identifying a position of a vehicle on a multi-layer road and for finding at which layer of a multi-layer road the vehicle (such as a vehicle driven by a user) is positioned.
As a tool for identifying or detecting a position of a vehicle by a user, various types of navigation system are known. FIG. 6 is a block diagram showing general features of a navigation system as known in the past. The navigation system shown in FIG. 6 comprises a GPS satellite 28, vehicle position calculating means 20 for calculating a position of a vehicle based on data from the GPS satellite 28, information retrieval means 23 for retrieving data such as a facility to be utilized, route searching means 21 for searching a route up to the facility, guiding means 22 for guiding the vehicle along the searched route, display control means 25 for displaying data on display means 26 such as liquid crystal display unit or CRT display, and a map data 27 stored in a storage medium such as CD-ROM.
Now, description will be given on measurement of the position of the vehicle based on the information from GPS satellite referring to FIG. 7 and FIG. 8. FIG. 7 shows an example, in which three GPS satellites in the sky can be seen from the vehicle. If this is represented in the sky chart shown in FIG. 8, the GPS satellites are seen at three different bearings or azimuths with respect to the advancing direction of the vehicle, and correct position measurement can be achieved in this case. Specifically, using azimuth of the vehicle and azimuth of the road, a correct road is identified by map matching. If the GPS satellites are under this condition, it is possible to correctly identify the position of the vehicle and the road where the vehicle is running.
However, when the vehicle is running on a road, which comprises two or more parallel roads constructed in multiple layers, it is difficult for a conventional type navigation system to identify the position on the road.
That is, on a road, which comprises two or more parallel roads and is constructed in multiple layers, there are an upper layer and a lower layer. Because the position of the vehicle projected on horizontal plane is the same, it is difficult to correctly identify on which of these layers the vehicle is located. As a result, when the user utilizes a highway map (a map for city expressway), audio guidance, or emergency information system, complete reliability is not always assured.
To solve the problems, it has been proposed to provide a gyro, which can detect pitching of the vehicle (whether it is ascending or descending in advancing direction). In this case, it is detected whether the vehicle has gone up on an ascending slope to enter a road on an elevated highway or has gone down on a descending slope to leave the elevated road, and it is judged whether the vehicle is running on a road (upper layer) constructed on the elevated highway, or it is running on a planar road (lower layer) under the elevated road. However, in order to accomplish this concept, it is necessary to install a new gyro, and this means higher cost for the navigation system.
To solve the above problems, it is an object of the present invention to provide a method for identifying a position of a vehicle on a multi-layer road, by which it is possible to identify whether the vehicle is running on upper layer or lower layer of the multi-layer road without using additional new devices or parts on the navigation system.
According to one aspect of the present invention, there is provided a method for identifying a position of a vehicle on a multi-layer road to identify whether the vehicle running on one of the layers of the multi-layer road is running on the uppermost layer or on a lower layer under the uppermost layer of the multi-layer road, whereby, in case the ratio of a distance in a section where GPS position measurement can be achieved in a predetermined traveling distance is equal to or higher than a predetermined threshold for identification of the upper layer, it is judged that the vehicle is running on the upper layer (the uppermost layer), and if the ratio is lower than the other predetermined threshold for identification of lower layer, it is judged that the vehicle is running on the lower layer (a layer under the uppermost layer). Thus, it is possible to provide effects to identify whether the vehicle is on the upper layer or the lower layer of the multi-layer road without using additional new devices or parts on the navigation system.
In the present specification, the term xe2x80x9cupper layerxe2x80x9d means the uppermost layer as described above, and the term xe2x80x9clower layerxe2x80x9d means a layer under the uppermost layer. That is, in case of 3-layer structure, the uppermost layer is the upper layer, and each of two layers under the uppermost layer is the lower layer.
According to another aspect of the present invention, there is provided a method for identifying a position of a vehicle on a multi-layer road to identify whether the vehicle running on one of the layers of the multi-layer road is running on the uppermost layer or on a lower layer under the uppermost layer of the multi-layer road, whereby, in case the section where GPS position measurement can be achieved in the predetermined traveling distance is discrete, it is identified as the lower layer, and it is possible to identify the lower layer of the multi-layer road without using additional new devices and parts on the navigation system.
According to still another aspect of the present invention, there is provided a method for identifying a position of a vehicle on a multi-layer road to identify whether the vehicle running on one of the layers of the multi-layer road is running on the uppermost layer or on a lower layer under the uppermost layer of the multi-layer road, whereby, if satellites at left and right are equally seen with respect to the advancing direction of the vehicle, it is identified as the upper layer, and if not, it is judged as the lower layer. Thus, it is possible to provide effects to identify the upper layer or the lower layer of the multi-layer road without using additional new devices or parts on the navigation system.
According to still another aspect of the present invention, there is provided a method for identifying a position of a vehicle on a multi-layer road to identify whether the vehicle running on one of the layers of the multi-layer road is running on the uppermost layer or on a lower layer under the uppermost layer of the multi-layer road, whereby, if a satellite above a lane in opposite direction with respect to the advancing direction of the vehicle is seen, it is judged as the upper layer, and if not, it is judged as the lower layer. Thus, it is possible to provide effects to identify the upper layer or the lower layer of the multi-layer road without using additional new devices or parts on the navigation system.
According to yet another aspect of the present invention, a method for identifying a position of a vehicle as described above can be provided, wherein if the level of receiving signal from a satellite above a lane in opposite direction with respect to the advancing direction of the vehicle is lower than the level of receiving signals from a satellite in reverse direction to the lane in opposite direction, it is judged the vehicle is running on an apparent upper layer and not on a true upper layer and there are provided effects that an apparent upper layer identified erroneously because of reflection from a building or the like is not identified as a true upper layer.